Sweep circuits



Aug. 9, 193a, E. Bas ET AL 2,126,243 SWEEP CIRCUITS I a 1 Filed May 2, 1936 Ju i INVENTOR fR/VST Ell-SSE JAN VAN DER MARK BY A L4 I/EN/S ATTORNEY Patented Aug. 9, 1938 UNITED s'rATE swear cmcm'rs Ernst Busse, Hamburg, Germany, and Jan van der Mark and Adolph Venis, Eindhoven, Netherlands, assignorsto N. V. Philips Gloeilampeniabrieken, Eindhoven, Netherlands, a corporation of the Netherlands Application May 2, 1936, Serial No. 77,646

In the Netherlands April 18, 1935 1': Claims. '(ci. 250-3 The invention relates to a device intended to generate a voltage which increases linearly with the time and comprising a condenser, a source of direct voltage anda resistance through which 5 the condenser is charged.

' Such a circuit-arrangement isichiefiy utilized in television transmitting and receiving systems which comprise a cathode ray tube and inwhich a device generating a saw-tooth current or voltm age is utilized for the control of the scanning movement of thebeam of cathode rays. In such systems it is desirable that the controlling volt-. age should increase linearly with the time.' The known controlling devices for generating a sawit tooth current or voltage comprise a condenser,

a source of direct'voltage and a resistance through which the condenser is charged by the source of direct voltage while a discharge tube connected in parallel with the condenser serves to discharge 20 the condenser periodically.

Turning now to the drawing, in which Fig. 1 illustrates diagrammatically a simplified circuit diagram for aiding in the explanation of our in-' vention 25 Fig. 2 shows diagrammatically a circuit em- .bodying our invention; and

Figs. 3 and 4 show schematically modifications of tlz e embodiment of our invention shown in Fig. a

Our invention will be explained in detail.

Such a known device for generating a sawtooth current or voltage is represented in Figure l oflthe accompanying drawing in which I denotes a source of voltage, 2 a condenser. 3 a discharge 35 tube-and4- a resistance through which the condenser 2 is charged.

The operation of such a circuit arrangement is as follows:

. The condenser 2 is charged by thesource of v 40 voltage I through a resistance 4 with a rapidity which isdetermined by the values of the resist ance B and of the condenser 2, until the ignition voltage of the discharge tube 3 which may containa control electrode is attained or until, as is The instantaneous value of the voltage set up across the condenser 2 increases during the charging period linearly with the time it the charging current oi the condenser 2 is constant.

To that-end it has prevlouslybeen proposed to charge the condenser 2 through a variable imgenerating a saw-tooth the initiation of the discharge.

pedance formed by a saturated diode or by a screen grid tube.

Where such type variable impedances are used, it is inexpedient to ground one pole of all the batteries, SmCG'ShOI'l} circuits would result. The 5 use of these additional-potential sources arises from the fact thatin addition'to the potential source for charging the condenser, a source of voltage must be supplied for heating the filament and in the case of a screen grid tube, biasing batteries must also be provided. Accordingly, the

voltage sources float above ground potential. Furthermore, the capacities oi said batteries v relatively to earth, form part of the :circuit which determines the frequency of the oscillations gen- 5 erated, with the result that the frequency which can. be obtained with the circuit-arrangement is decreased. v I

The object of the invention is to provide a device for generating a voltage which increases linearly with the time and to obviate the above mentioned disadvantages. This is obtained in the circuit-arrangement according to the invention owing to the iactfth'at in the charging circuit operates an emf. derived from the condenser voltage and being equal and oppositely directed to the condenser voltage.

In'one particular'mode of realization of the circuit-arrangement according to the invention the emf. derived from the condenser is taken from the anode circuit of the last tube of an even number of cascade-connected discharge tubes to which the voltage set up across the condenser is applied.

The emf. derived from the condenser may likewise be taken from the anode circuit of the last'oi an odd number of cascade-connected discharge tubes it an odd number of these tubes are formed by a ,multi-grid tube whose electrode voltages are'adiusted in such manner that in the anode circuit of the multi-grid tube is set up avoltage which 'is in phase with the voltage supplied to the grid.

Figure 2 represents a circuit-arrangement for voltage required for 5 scanning purposes in television systems, comprising a condenser '2; a source I of direct volt age and a resistance 4 through which the condenser 2 is charged by the source -I of direct voltage. The condenser discharges periodically through a charge tube '3, periodical impulses being supp ed to the grid of said tube to control The voltage set up across the condenser 2 is'supplied through a condenser E to a discharge tube 8 between the i the anode circuit of the tube 6 is applied via' voltage set up across the condenser 2 increases linearly with the time, the voltage produced in grid condenser 1 and a leakage resistance In to the grid of a tube I I in the anode circuit of which is located a resistance ii a point I! of which is connected to that end of the resistance 4 which is remote from the condenser 2. with the aboveincreases linearly with the described circuit-arrangement that portion of the resistance I! which is located between the point II and the positive terminal. of the source of voltage I is included in the charging circuit which comprises the source of voltage I (which acts at the same time as the source of anode voltage for the tubes 6 and II) the resistance 4 and the condenser 2. According to the invention, the point I! is so chosen that the voltage set up across said portion of the resistance I2 is equal to the voltage produced across the condenser 2. The direction of the voltage set up across said portion of the resistance 12 in the charging circult is opposite to the condenser voltage.

with the circuit-arrangement described it is ensured that during the chargingperiod the voltage set up across the condenser increases linearly with the time. follows:

.In the c'harging circuit applies the equation +E=e:+ 4+ n, in which E denotes the voltage of the sourcel of direct voltage, en the voltage.

set up across the condenser 2, er the voltage across the resistance -4 and 812' the voltage across that portion' of the resistance I! which is included in the charging circuit. If in this equation during the charging period e2=-n, or in other words if in the charging circuit a voltage is operative which is equal and, oppositely directed to the condenser voltage, which may be obtained by anadequate choice of the number of stages of amplification connected alter the condenser and by the correct adjustment of the point II, the voltage e4 across the resistance at is constant during, this period. In this case the condenser is charged with a constant current with the result that the voltage across the condenser increases linearly with the time.

In the circuit-arrangement described it is possible, however, that due to the presence of the condenser I and of the resistance I the increase of the voltage with the time is not completely linear. This is caused by thefact that with a view to the tube 6 the resistance I may not be taken of any desired high value. In this case the current flowing through the resistance 1 is no longer negligible with respect to the charging current. According to the invention, this drawback can be removed by adjusting the point ii of the resistance II in such manner that the emf. acting in theohlrflnl circuit is equal to the condenser voltage multiplied by wherein R1 and Rs denote the values of the resistances 4 and I rapectively.

adiustmento! the point I! the condenser voltage time ensues from the The explanation thereof is as- That with this 4 wherein 1: denotes the voltage 0! the source I of direct voltage, ii the charging current of the condenser I, i: the current flowing through the grid leakage resistance I. i the current flowing through the resistance 4, e: the voltage across the "condenser 2, en the voltage across that portion of the resistance It which is included in the charging circuit, er the value of the voltage across the resistance 4 and ea-the value of the voltage across the grid leakage resistance I. 4

From the Equations (1), (2) and (3) may be deduced:

If in this equation during the char ing period the charging current of the condenser 2 is constant during this period with the result that the 'voltage of the condenser increases linearly with the time.

Another measure which may be utilized in accordance with the invention in order to compensate the deflection produced by the resistance I consists in connecting a point located between the ends of the grid leakage resistance I to a point which has relative to the cathode a voltage which is equal to and in phase with the voltage set up'between the grid and the cathode of the tube 6. In this case the current flowing through the resistance I remains zero at every moment and can consequently no longer act on the char ing current of the condenser 2. Besides, owing to this measure the condenser 5 may be taken much smaller without any influence being exerted on the shape of the curve representing the instantaneous value of the voltage as a function of the-time. The voltage to be supplied to the point located between the ends of the leakage resistance I may be taken from the anode circuit of one of the discharge tubes in the circuitarrangement.

One mode of realization of a device for generating a saw-tooth voltage in which the above mentioned measure has been carried out is represented in Figure 3 in which between a point I4 of the resistance I and the cathode of the tube 6 is applied a voltage which is equal to and in phase with the voltage set up between the grid and the cathode of the tube 4, owing to the fact that the point I4 is connected through a blocking condenser II to that end of the resistance 4 which is connected to the anode circuit of the tube ii. For the rest the circuit-arrangement is completely similar to the circuit-arrangement of Figure 2. An advantage of the last-mentioned measure of compensating for the influence of the grid leakage resistance I relatively to the first-mentioned .measure is that it is independent of the value of impulses 'whic'h'cause the condenser 2 to discharge. The saw -tooth voltage set up across the condenser 2 is suppliedinknown manner to the tubes 6 and II connected in cascade. The grid of the tubes is connected to sucha point'oi the output circuit of the tube 6 that the saw-tooth control the beam of cathode rays.

sired, the deflecting plates, instead of being convoltage of the grid of'the tube 5 relative to the cathode with the result that in the output circuits of the tubes 6 and ii across the resistances 8 and voltages are set-up which are equal to and in counterphase with each other. Each of the ends a of the resistances 8 and" I2 which are connected to the anode of the corresponding tube is connected, to cheat the deflecting plates i6 and ii of a cathode ray tube, said plates being destined to If it is denected directly across the resistors 8 and I2 may be connected by condensers inserted in series with the connection between the plates and the resistors and a leakage resistor connected directly across the plates l6 and 11. In the circuitarrangement described the voltage in the median plane between .the deflecting plates is constant as is desired with cathode ray tubes in order to prevent distortion of the picture received.

' In order to ensure inithe circuit-arrangement described that the voltage between the plates i6 and i1 increases linearly with the time, an emf. which is equal to and has the opposite direction of the condenser voltage is taken from the anode circuit of the tube ll owing to the fact that a point i3 of the resistance i2 is connected to that end of the resistance 4 which is remote from the condenser 2. If desired, the influence of there sistance i in this circuit-arrangement may be suppressed by adjusting the point IS in such manner that the voltage between this point and "the "end of the resistance l2 which is connected to the positive terminal of the source of direct" voltage is equal to the voltage set up across the condenser 2 multiplied by the factor Preferably, however, a voltage which is equal to and in phase with the voltage set up between the grid and the cathode of the tube 6 is applied between a point of the grid leakage resistance-i, and the cathode of the tube 6 by connecting the end of the resistance 4 which is remote from the condenser-E through a condenser late a point of the grid leakage resistance 1. I

' and means to decrease the potential drop of only the impedance in proportion to the potential rise of the condenser.

3. A. sweep oscillator comprising a source of voltage, a condenser, a resistance, an impedance,

means to connect all of said elements inseries, and

feedback means to maintain the potential drop across the resistance independent of the con denser voltage.

Having described our invention, what we claim 1. A sweep oscillator comprising a source of 4. A sweep oscillator comprising a source oi voltage, a condenser, a resistance, an impedance, means to connect all of said'eler'nents. in series, whereby energy is stored in the condenser with a consequential rise in potential thereacross, and means to vary the voltage across the impedance in an equal and opposite fashion to the variation of voltage across the condenser.

5. A sweep oscillator comprising a source of voltage, a condenser, a resistance, an impedance, means to connect all of said elements in' series, whereby energy is stored in the condenser, means to supply input energy to thermionic amplifier in accordance with the energy stored in the condenser, and means to impress upon the imped ance energy from the thermionic amplifier.

6. A sweep oscillator comprising a source of v voltage, a condenser, a resistance, an impedance,

circuit of the amplifier in accordance with the energy stored inthe condenser, and means to connect the output circuit of the amplifier to the impedance;

'l. A sweep oscillator comprising a source of voltage, a condenser, a resistance, an impedance,

means to connect all of said elements in series, whereby energy is storedin the condenser with a consequential rise in potential thereacross, an

even number of amplifying stages connected in cascade, an input circuit and an output circuit for the cascade connected stages, means to supply energy to the input circuit in accordance with the-voltage developed across the condenser, and means to connect the output circuit across the impedance.

8. A sweep oscillator comprising a source of voltage, a condenser, a resistance, an'impedance, means to connect all of said elements in series, whereby energy is stored in the eondenserwith a consequential rise in potential thereacross, an even number of amplifying stages connected in cascade, an input circuit and an output circuit for the cascade connected stages, means to supply energy to the input circuit in accordance with the voltage developed across the condenser,

means to connect the output circuit across the impedance, and means to adjust thevoltage developed across the impedance to equal the voltage developed across the condenser.

9. A sweep oscillator comprising a source of voltage, a condenser, a resistance, an impedance,

means to connect all of said elements in series, whereby energy is stored in the condenser with a consequential rise in potential thereacross, an

even number of amplifying stages connected in cascade, a serially cemented condenser and resistance input circuit for the cascade connected stages, an output circuit for the cascade connected stages, means to supply energy to the input circuit in accordance with the voltage developed across the condenser, and means to connect the output circuit across the impedance, and means to adjust the voltage developed across the impedance to equal the voltage developed across the condenser multiplied by one plus the ratio of the resistance connected 'in series with the condenser to the resistance in the input circuit,

'10. A sweep oscillator comprising a source of means to connect all 01' said elements in series,

voltage, a condenser, a resistance, an impedance,

consequential rise .in potential thereacross, an even number of amplifying stages connected in cascade, a serially connected condenser and resistance input circuit for the cascade connected stages, an output circuit for the cascade connectoutput circuit across the impedance, and means to adjust the voltage developed across the impedance to equal the voltage developed across the condenser multipliedby one plus the ratio of the resistance connected in series with the condenser to the resistance in the input circuit. 11. A sweep oscillator comprising a source of voltage, a condenser, a resistance, an impedance, means to connect all of said elements in series, means to vary the potential drop across only the impedance as a function of the stored energy of the condenser, and a discharge tube. connected across the condenser.

12. A sweep oscillator comprising a source of voltage, a condenser, a resistance, an impedance,

means to connect all of said elements in series,

' whereby energy is stored in the condenser, means to drive a thermionic amplifier in accordance with the energy stored in the condenser, means to impress upon the impedance energy from the thermionic amplifier, and 'a discharge tube connected across the condenser.

13. A sweep oscillator comprising a two stage resistance-capacity coupled thermionic amplifier,

'having an input and an output circuit, a concondenser for storing energy, the method of .gen-

erating a voltage which increases linearly with respect to time, which comprises the steps of pro; dudm a source of voltage, charging the condenser from the source of voltage thereby producing a potential drop across the condenser, amplifying the produced potential drop, deriving a portion of the amplified potential drop, and injecting the derived potential drop in series with the condenser and the source of voltage.

15. In a sweep oscillator wherein is provided a condenser for storing energy, the method of generating a voltage which increases linearly with respect to time, which comprises the steps of producing-a source of voltage, charging the condenser from the source of voltage thereby producing a potential drop across the condenser, amplifying the produced potential drop, deriving a portion of the amplified potential drop equal to the potential drop across the condenser, and injecting the derived potential drop in series with the condenser and the source of voltage.

16. In a sweep oscillator wherein is provided a condenser for storing energy, the method of generating a voltage which increases linearly with respect to time, which comprises the steps of producing a source of voltage, charging the condenser from the source of voltage thereby producing a potential drop acrossthe condenser, amplifying the produced potential drop, deriving a portion of the amplified potential drop equal to the potential drop across the condenser, and injecting the derived potential drop in series with the condenser and source of voltage and in opposite polarity to 1 the potential drop across the condenser.

17. In a sweep oscillator wherein is provided a condenser for storing energy, the method of generating saw-tooth voltage waves which comprises the steps of producing a source of voltage, charg- I ing the condenserfrom the source of voltage thereby producing a potential drop acrossthe condenser, amplifying the produced potential drop, deriving a portion of the amplified potential drop equal to the potential drop across the condenser, injecting the derived potential drop in series with the condenser'and source of voltage and in opposite polarity to the; potential drop across the condenser, and periodically discharging the condenser.

- ERNST BUSSE.

JAN var: nrs ADOLPH VENIS. 

